1. Field of Use
This invention relates generally to optical switching methods and apparatus, and more particularly to optical switching methods and apparatus that achieve optical gain in silicon.
2. Description of the Related Art
Communication networks increasingly rely upon optical fiber for high-speed, low-cost transmission. Optical fibers were originally envisioned as an optical replacement for electronic transmission media, such as high-speed coaxial cable and lower-speed twisted-pair cable. However, even high-speed optical fibers are limited by the electronics at the transmitting and receiving ends, generally rated at a few gigabits per second, although 40 Gb/s systems have been prototyped. Such high-speed electronic systems are expensive and still do not fully exploit the inherent bandwidth of fiber-optic systems, measured in many terabits per second.
All-optical transmission systems offer many intrinsic advantages over systems that use electronics within any part of the principal transmission path. Wavelength-division multiplexing (WDM) electronically impresses different data signals upon different carrier frequencies, all of which are carried by a single optical fiber. The earliest WDM systems did not provide optical switching but only point-to-point WDM.
To achieve optical gain in a semiconductor metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy processes have been used to produce complex nanostructures of layered materials such as InGaAs, InGaAsP and InGaAsN. These direct band gap semiconductor materials belonging to group III and V columns of the periodic table of elements are well known sources for LEDs, Lasers, and optical amplifiers. However, these materials make inferior quality high sensitivity photon detectors at fiber communication wavelengths.
It would be desirable to have silicon based lasers, LEDs and optical amplifiers because such devices would help to resolve the difficulties of integrating optical and electronic functions on a single chip. The high thermal conductivity of silicon can result in operational advantages. However, up to now efforts to obtain silicon based LEDs, lasers and amplifiers, especially devices that operate at wavelengths from about 1.3 or 1.5 μm, have not been successful.
There are currently three common methods of doping rare-earth ions into a silicon lattice. These methods are, (i) doping by growth of amorphous material from a silicon/rare-earth compound, (ii) doping by chemical vapor deposition and (iii) ion-implantation and rapid thermal anneal. The potential of utilizing rare-earth ions in a semiconductor matrix for the development of LED's and lasers, has been reported by H. Ennen, et al., Applied Physics Letters, Vol. 43, page 943 (1983). It has also been observed that the presence of oxygen in erbium-doped silicon can increased erbium photoluminescence, P. M. Favennec et al., Japanese Journal of Applied Physics, Vol. 29, page L524, (1990)].
Attempts to produce optical gain by the use of rare earths or the inclusion of materials in silicon have also been disclosed in U.S. Pat. Nos. 5,646,425; 5,119,460; 4,618,381; 5,634,973; 5,473,174; and 5,039,190.
However, efforts to create a commercially viable silicon based rare-earth doped LED, laser or optical amplifier have not been successful due at least in part to the fact that the observed luminescence has been too weak to support such a device. Even when weak gain was observed, the radiative lifetimes measured were six orders of magnitude longer than those exhibited by InGaAs devices, making the doped or implanted silicon structures inadequate for telecommunication applications.
There is a need for silicon based, rare-earth containing, optical devices that have sufficient luminescence and strong gain. There is a further need for silicon based, rare-earth containing optical devices that can switch the separate WDM channels, carrier frequencies, in different directions without the necessity of converting optical signals to electronic signals. There is yet a further need for silicon based, rare-earth containing optical devices that are integrated on the same monolithic chip as associated support circuitry. Yet there is another need for silicon based, rare-earth containing optical devices that amplify and/or attenuate light in preferred telecommunications wavelengths, including but not limited to 1250 to 1650 nm. Still there is a further need for silicon based, rare-earth containing optical devices that use avalanche multiplication effects of silicon coupled with sufficient optical gain due to the presence of an optically active rare-earth ion.